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More on Cassegrainians and Their Construction |
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by Albert G. Ingalls |
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So now is the time for all good amateurs (who can) to make a Cassegrainian or a Gregorian, and while we are at it let's have a little fun out of it. It is therefore pro- posed to organize a new society, on world-wide lines, and for short call it the "Cassegrainian Club," and it is our secret purpose to run it strictly by Tammany Hall methods. Accordingly we have fixed up the following slate of officials of the proposed club, on which all Cass-Greg specialists are invited to vote. (All adverse votes will be thrown out by the election committee-we can't have any dissension.) King Cassegrain-John M. Pierce, who about six years ago made the first American amateur's Cassegrainian we know of (see photograph ). Crown Prince-R. W. Porter, who made the next one. Patron Saint-J. H. Hindle. Duke-Horace E. Dall, also of England, whose new Cassegrainian is described below. This is as far as we self-appointed politicians could get in the matter of selecting officers, because no other eligible candidates were known-none had made Cassegrains. However, we suppose we will need a few more potentates such as counts and barons, and here is an opening for some aspiring young man to become royalty. All the other members will be rated as mere slaves, villains, and churls, unless we can think up enough offices to go around. Those who complete compound telescopes may select and name their own office. This is to be the only club on earth with no by-laws, no constitution, no initiation fee, and no dues. It will be very (oh very) exclusive and very high-hat. As the present writer never has made a compound telescope he cannot be a member, but will sit outside the lodge door and shiver. If anyone can prove completion of jobs prior to those of the potentates, the latter will be duly deposed, demoted, and beheaded. Until an aspirant establishes proof of completing a compound telescope he will be entered on the books as a basement member and regarded as some lowly form of life-just protoplasm. Mr. Hindle's monograph is still available to those who will promise to return it promptly. Let's go! HERE is what Mr. Dall, who is a professional maker of optical work, especially one-piece Tolles eyepieces, writes from 186 Dunstable Road, Luton, Bedfordshire, England concerning his Cassegrain: "I believe I am correct in saying that my latest telescope-just completed-is by far the smallest and lightest telescope of its aperture and power and quality of performance in the world. The clear aperture is 6 inches. The overall length, including eyepiece, is 19 inches, and the weight complete with finder and all is only 5-1/2 pounds. The image is erect, as I intended it primarily for terrestrial work, and the eyepiece gives a comfortable eyepoint and wide angle of view, with no small eyeholes as on Gregorian telescopes. "The construction is a modified Cassegrainian, and the angle of the final image is relatively narrow, that is f.l3, enabling ordinary eyepiece to behave well and high powers to be comfortably applied. Focusing is by rack and pinion-you can see the handwheel just under the tube. The focusing range is from 20 feet to infinity. "The tube is of stout seamless aluminum tubing and the whole is finished with a beautiful light blue gray crystalline enamel. In the photograph it is shown mounted on portable equatorial stand which is supposed to carry a 3-inch refractor. The small weight and moment of inertia of the present telescope enables this stand to mount it far more rigidly than the original 3-inch refractor. Hand pressure causes vibration on the latter which takes several seconds to die down, whereas similar pressure on the 6-inch causes vibrations which are damped down almost instantly. The short tube gives other advantages. Wind pressure is reduced, and the effects of tube currents are minimized. Moreover, the eyepiece is so close to the declination and R. A. axis that the height and position of the former does not vary more than a few inches for all parts of the sky. "Naturally the accuracy of figuring the optical surfaces must be extremely high for a telescope as short as this, but I have succeeded well in this and can resolve double stars down to the limit of the aperture. "The mirrors were lacquered with a coat much less than 1/25,000 inch thick on a whirling table, and this should last well for years." HERE are a few odds and ends: Has anyone made a built-up (cemented) glass disk and has it proved satisfactory? Several misguided workers have requested the "conductor" of the present department to publish his photograph. Being a victim of the shrinking violet complex he cannot accede to this ghastly request, but in case of really dire need see "A.T.M." page 35, the larger of the two figures. The attendance at the Adler planetarium in Chicago is now way past the million mark. They say that a fair share of those who witness this performance make immediate tracks for the nearest astrologer and have their horoscopes cast by the same stars. And this is the age of science! The planetarium for Los Angeles has been held up by a legal squabble, but St. Louis is soon to have one. Hale spectrohelioscopes are now in use or have been ordered by the widely distributed stations listed below. All these are professional; there is not as yet a single spectrohelioscope made by an amateur. Mr. Gustavus Wynne Cook of Wynnewood, Pennsylvania, an amateurastronomer (the possessor of a 30-inch reflector by Fecker!) owns one but did not make it himself. Spectroscopes are in operation at the Royal Observatory at Greenwich, England; Department of Solar Physics at Cambridge University, England; Federal Observatory at Zurich, Astrophysical Observatory at Florence, American College at Beirut, Syria; Observatory of Solar Physics at Kodaikanal, South India; Carnegie Institution, at Watheroo, Australia; National Institute of Astronomy at Nanking, China; Commonwealth Solar Observatory at Canberra, Australia; Dominion Observatory at Wellington, New Zealand; Apia Observatory at Apia, Samoa; Mt. Wilson Observatory at Pasadena, California; Pomona College at Clairmont, California; University of South Dakota at Vermilion; Yerkes Observatory at Williams Bay, Wisconsin, Adler Planetarium at Chicago; Ohio State University at Columbus; Carnegie Institution at Huancayo, Peru; Vassar College at Poughkeepsie, New York; Bell Telephone Laboratories, New York; Massachusetts Institute of Technology at Cambridge; Franklin Institute at Philadelphia. Several others are likely to be put in use and, according to Dr. George Ellery Hale, a general scheme of co-operation for the detection of eruptions on the sun's disk will be organized. Will some enterprising amateur please make a spectrohelioscope? Are we to let these mere professionals get ahead of us in this manner? The situation is scandalous.
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